The present disclosure relates to systems and methods for monitoring drilling fluids and, more specifically, for measuring the gas content in drilling fluids in real time using optical computing devices.
During the drilling of a hydrocarbon-producing well, a drilling fluid or “mud” is continuously circulated from the surface down to the bottom of the wellbore being drilled and back to the surface again. The drilling fluid serves several functions, one of them being to transport wellbore cuttings up to the surface where they are separated from the drilling fluid. Another function of the drilling fluid is to provide hydrostatic pressure on the walls of the drilled borehole to prevent wellbore collapse and the resulting influx of gas or liquid from the formations being drilled.
Analyzing the drilling fluid as it returns to the surface is recognized in the oil and gas industry as an important first appraisal of a potential hydrocarbon-bearing reservoir zone, thereby providing important data to guide subsequent evaluation and testing. Such analysis and testing is commonly referred to as “mud logging” analysis. Through mud logging, reservoir zones can be evaluated while they are being initially penetrated, thereby substantially preventing post-drilling changes to the formation that can limit the effectiveness of many other evaluation techniques.
Mud logging often includes the measurement and analysis of formation gases present in the drilling fluid as it returns to the surface. Such analysis can be valuable in providing data on the hydrocarbon and non-hydrocarbon gas species that may be encountered while drilling. Specifically, knowing the presence and concentration of hydrocarbon and non-hydrocarbon gases in drilling fluids provides an indication of the formation confronted by the drill bit and provides a basis for determining the feasibility of obtaining hydrocarbons from the well. The information that such analysis provides is vital in the planning and development of hydrocarbon reservoirs, as well as in the assessment of a reservoir's capacity and performance.
Mud logging analysis of drilling fluids is typically conducted off-line using laboratory analyses which require the extraction of a sample of the drilling fluid and a subsequent controlled testing procedure usually conducted at a separate location. Depending on the analysis required, however, such an approach can take hours to days to complete, and even in the best case scenario, a job will often be completed prior to the analysis being obtained. Although off-line, retrospective analyses can be satisfactory in certain cases, they nonetheless do not allow real-time or near real-time analysis capabilities. As a result, proactive control of drilling operations cannot take place, at least without significant process disruption occurring while awaiting the results of the analysis. Off-line, retrospective analyses can also be unsatisfactory for determining true characteristics of a drilling fluid since the characteristics of the extracted sample of the drilling fluid oftentimes change during the lag time between collection and analysis, thereby making the properties of the sample non-indicative of the true chemical composition or characteristic.